High pressure catheter balloon

ABSTRACT

A balloon formed of a single layer of polybutylene terephthalate and polytetramethylene ether glycol terephthalate copolymer in a substantially unblended form. The copolymer has a flexural modulus of greater than about 150,000 psi. The presently preferred copolymer is Hytrel® 8238 by DuPont. The balloon would be substantially unblended, defined as greater than about 60% by weight to about 100% by weight of the copolymer. The balloon is formed in a series of molds. The balloon exhibits high rupture pressure and low compliance coupled with good lesion cross and recross ability.

BACKGROUND OF THE INVENTION

This invention generally relates to intravascular catheters, such asballoon dilatation catheters used in percutaneous transluminal coronaryangioplasty (PTCA).

PTCA is a widely used procedure for the treatment of coronary heartdisease. In this procedure, a balloon dilatation catheter is advancedinto the patient's coronary artery and the balloon on the catheter isinflated within the stenotic region of the patient's artery to open upthe arterial passageway and thereby increase the blood flow therethrough. To facilitate the advancement of the dilatation catheter intothe patient's coronary artery, a guiding catheter having a preshapeddistal tip is first percutaneously introduced into the cardiovascularsystem of a patient by the Seldinger technique through the brachial orfemoral arteries. The catheter is advanced until the preshaped distaltip of the guiding catheter is disposed within the aorta adjacent theostium of the desired coronary artery, and the distal tip of the guidingcatheter is then maneuvered into the ostium. A balloon dilatationcatheter may then be advanced through the guiding catheter into thepatient's coronary artery until the balloon on the catheter is disposedwithin the stenotic region of the patient's artery. The balloon isinflated to open up the arterial passageway and increase the blood flowthrough the artery. Generally, the inflated diameter of the balloon isapproximately the same diameter as the native diameter of the body lumenbeing dilated so as to complete the dilatation but not over expand theartery wall. After the balloon is finally deflated, blood flow resumesthrough the dilated artery and the dilatation catheter can be removedtherefrom.

To reduce the restenosis rate and to strengthen the dilated area,physicians frequently implant an intravascular prosthesis, generallycalled a stent, inside the artery at the site of the lesion. Stents mayalso be used to repair vessels having an intimal flap or dissection orto generally strengthen a weakened section of a vessel. Stents areusually delivered to a desired location within a coronary artery in acontracted condition on a balloon of a catheter which is similar in manyrespects to a balloon angioplasty catheter, and expanded to a largerdiameter by expansion of the balloon. The balloon is deflated to removethe catheter and the stent left in place within the artery at the siteof the dilated lesion. See for example, U.S. Pat. No. 5,507,768 (Lau etal.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporatedherein by reference.

To properly position the balloon within the stenotic region, the balloonmust be advancable within the patient's tortuous vasculature.Additionally, the balloon must be advanced across the stenosis,typically referred to as the ability to cross the stenosis. However, thedesign of balloon catheters must balance the competing concerns offlexibility and balloon softness required for trackability andcrossability with balloon strength and low compliance required to expandagainst the stenosis.

Therefore, what has been needed is a balloon catheter with improvedtrackability, crossability and strength. The present invention satisfiesthese and other needs.

SUMMARY OF THE INVENTION

The invention is directed to a balloon formed of a single layer of asubstantially unblended copolymer having a flexural modulus of at least150 kpsi (1 GPa). A single layer is defined as one layer of copolymerused to manufacture the balloon. The copolymer is a copolymer ofpolybutylene terephthalate (“PBT”) and polytetramethylene ether glycolterephthalate (“PTMEGT”).

In a presently preferred embodiment, the copolymer is substantiallyunblended with any other material. Substantially unblended, for thepurpose of this patent is defined as greater than about 60% by weight ofthe copolymer. In a more preferred embodiment, the balloon is formed ofno less than about 95% by weight of the copolymer. The most preferredembodiment is about 100% by weight PBT and PTMEGT copolymer. Suitablepolymeric materials for blending with the PBT and PTMEGT copolymerinclude polymers such as polyethylene terephthalate or polybutyleneterephthalate to make a stiffer balloon.

A balloon catheter of the invention generally comprises a catheterhaving an elongated shaft with proximal and distal ends, an inflationlumen, and a single layered balloon formed of a copolymer made ofpolybutylene terephthalate and polytetramethylene ether glycolterephthalate. A suitable PBT and PTMEGT copolymer includes Hytrel®polymers from E.I. DuPont de Nemours and Company. Hytrel® is availablein a range of grades. Properties of the grade are determined by theratio of PTMEGT to PBT. The presently preferred copolymer is Hytrel®8238, which has a shore durometer hardness of 82D.

In accordance with the invention, the balloon is formed of a polymericmaterial, whether 100% copolymer or substantially unblended, thepolymeric material having a flexural modulus of greater than about 150kpsi (1 GPa). The flexural modulus is a measure of the ratio of stressto strain during flexural deformation. Therefore, a high flexuralmodulus number means a material is harder to distort with increasingforce. Preferably, the copolymer has a flexural modulus of at least 175kpsi (1.17 GPa).

The material will have an elongation at break of at least about 200%,preferably about 350% or higher. The tensile strength of the material atbreak will be at least 5500 psi, preferably greater than about 6500 psi(45 MPa). The tensile strength for the most preferred material is about7000 psi (48 MPa) or higher. The balloon made from the material willhave an average rupture pressure of at least 18 atm, and is usuallyabout 22 atm to about 26 atm for a balloon with a double wall thicknessof about 0.0016 inches (0.04 millimeters).

The balloon of this invention will have a low compliance. The termcomplaint is understood to mean the measure of the increase in diameterof the balloon under pressure. Low compliance is meant to imply radialexpansion less than about 0.045 millimeters per atmosphere of pressureapplied (mm/atm). In the most preferred embodiment of the invention, theresulting balloon has a compliance of less than 0.02 mm/atm within theworking range of the balloon of about 10 atm to about 18 atm.

Various designs for balloon catheters well known in the art may be usedin the catheter of the invention. For example, the catheter may be aconventional over-the-wire dilatation catheter for angioplasty having aguidewire receiving lumen extending the length of the catheter shaftfrom a guidewire port in the proximal end of the shaft, or a rapidexchange dilatation catheter having a short guidewire lumen extending tothe distal end of the shaft from a guidewire port located distal to theproximal end of the shaft. Additionally, the catheter may be used todeliver a stent mounted on the catheter balloon.

The balloon of the invention provides improved performance because ofthe strength of the material coupled with its unexpected tracking andcrossing ability. The catheter of the invention has the unexpectedability to track as well as a catheter with a balloon formed of a morecompliant material with a lower flexural modulus. Tracking is the easethat the balloon catheter moves through the blood vessel and advancedover the guidewire. Good tracking ability means the user feels lessresistance. In addition, the balloon of this invention could cross alesion which Nylon and Pellethane balloons known in the art could notcross. The balloon of this invention, once deflated, also had theability to recross the lesion after initial dilation. Therefore, theballoon of this invention would make an excellent choice for physiciansdealing with multiple stenosis and re-dilation cases.

The material properties of the balloon also make the invention ideal forstent implantation. The balloon has low compliance, coupled with highpressure capability. Therefore, the balloon of this invention would beused for a balloon catheter to cross a non-dilated lesion and expand tosimultaneously dilate the lesion and implant the stent.

These and other advantages of the invention will become more apparentfrom the following detailed description of the invention and theaccompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, partially in section, of a ballooncatheter that embodies features of the invention, showing the balloon inan unexpanded state.

FIG. 2 is a transverse cross sectional view of the catheter of FIG. 1taken along lines 2—2.

FIG. 3 is a transverse cross sectional view of the catheter of FIG. 1taken along lines 3—3.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1-3, the catheter 10 of the invention generallyincludes an elongated catheter shaft 11 having a proximal section 12 anddistal section 13, an inflatable balloon 14 formed of substantiallyunblended PBT and PTMEGT copolymer on the distal section 13 of thecatheter shaft 11, and an adapter 17 mounted on the proximal section 12of shaft 11 to direct inflation fluid to the interior of the inflatableballoon. The embodiment shown in FIG. 1 includes a stent 16 disposedabout the balloon 14. FIGS. 2 and 3 illustrate transverse cross sectionsof the catheter shown in FIG. 1, taken along lines 2—2 and 3—3respectively.

In the embodiment illustrated in FIG. 1, the intravascular catheter 10of the invention is an over-the-wire catheter, and is illustrated withina patient's body lumen 18 with the balloon 14 in an unexpanded state.The catheter shaft 11 has an outer tubular member 19 and an innertubular member 20 disposed within the outer tubular member and defining,with the outer tubular member, annular inflation lumen 21. Inflationlumen 21 is in fluid communication with the interior chamber 15 of theinflatable balloon 14. The inner tubular member 20 has an inner lumen 22extending therein, which is configured to slidably receive a guidewire23 suitable for advancement through a patient's coronary arteries. Thedistal extremity of the inflatable balloon 14 is sealingly secured tothe distal extremity of the inner tubular member 20 and the proximalextremity of the balloon is sealingly secured to the distal extremity ofthe outer tubular member 19.

The catheter 10 is advanced within the patient's vasculature. Theballoon 14 on a distal section 13 is then positioned so that at least alength of the balloon is across a non-dilated region within thepatient's vasculature. The balloon 14 is then expanded against thepatient's lumen 18 to simutaneously dilate the undilated lesion andimplant the stent 16.

The balloon 14 of the invention is formed of a single layer of PBT andPTMEGT copolymer. Preferably, the PBT and PTMEGT copolymer is arandomized block copolymer. Such presently preferred copolymers areHytrel® copolymers provided by DuPont. Additionally, the preferredcopolymer would have a hardness, Shore D scale of greater than about 72,preferably about 82. The copolymer is substantially unblended, definedearlier as having greater than about 60% by weight, preferably greaterthan about 95% of the PBT and PTMEGT copolymer.

The balloon 14 generally has a flexural modulus of greater than about150 kpsi (1 GPa), preferably about 150 kpsi (1 GPa) to about 300 kpsi (2GPa). Most preferably not less than about 175 kpsi (1.17 GPa). Thecompliance of the balloon 14 is less than 0.045 millimeters peratmosphere, and preferably less than 0.02 millimeters per atmosphere.

Balloon 14 has an average burst pressure of not less than about 270 psito about 400 psi. Preferably, the average burst pressure is greater thanabout 330 psi. The wall hoop strength of balloon 14 is not less thanabout 20 kpsi, with a double wall thickness of at least 0.0007 inches(0.017 millimeters) to about 0.0025 inches (0.06 millimeters).Preferably, the double wall thickness is between 0.0015 (0.038millimeters) and 0.0018 inches (0.046 millimeters) for a 3.0 millimeterdiameter balloon.

The balloon is typically formed by extruding the polymer material toform a polymeric tube. The tube is placed in a balloon mold and exposedto elevated temperature and pressure to form the balloon. Both internalpressure and axial tension are applied to the polymer material. In apresently preferred embodiment, the balloon is formed by expanding thetube in two or more successively larger molds. The temperature may stayconstant or be increased at each mold. Most preferably, the series willencompass at least three molds. Each successive mold will increase theradius of the mold. This process will prevent abrupt increases in wallhoop stress during balloon blowing.

Typically, the first mold increases the polymeric tube to about 30%-60%of the final diameter of the finished balloon The second mold increasesthe polymeric tube to about 60%-90% of the final diameter of thefinished balloon. The third mold has an inner diameter approximatelyequal to the outer diameter of the finished balloon. However, the numberof molds, and the successive sizes are variable, based on the blend ofcopolymer used and the final diameter of the balloon.

EXAMPLE

A 3.0 mm balloon was made from 100% copolymer uses a three mold process.The balloon was 100% Hytrel 8238. The first mold expanded the tube to a1.5 millimeter diameter. The mold exposed the tubing to a pressure ofabout 500 psi at a temperature of about 110° C. The second moldincreased the diameter to 2.0 millimeters, but only employed a pressureof about 200 psi to about 400 psi at about 120° C. The final blow moldused a pressure of 500 psi to increase the balloon to its final diameterof 3.0 millimeters at about 130° C.

The resulting 3.0 millimeter balloon had compliance of 0.014 mm/atm. Thedouble wall thickness was 0.0016 inches (0.04 millimeters). The balloonalso had a wall hoop strength of 26.8 kpsi, and an average burstpressure of 383 psi.

Although individual features of embodiments of the invention may beshown in some of the drawings and not in others, those skilled in theart will recognize that individual features of one embodiment of theinvention can be combined with any or all the features of anotherembodiment.

What is claimed is:
 1. An inflatable single layered balloon for amedical device comprising a polymeric material, the polymeric materialbeing a substantially unblended copolymer of polybutylene terephthalateand polytetramethylene ether glycol terephthalate, the copolymer havinga flexural modulus of greater than about 150,000 psi.
 2. The singlelayered balloon as in claim 1 wherein the copolymer is a randomizedblock copolymer.
 3. The single layered balloon as in claim 1 wherein thecopolymer has a hardness, shore D scale, of greater than about
 72. 4.The single layered balloon as in claim 1 wherein the copolymer has ahardness, shore D scale, of about 72 to about
 82. 5. The single layeredballoon as in claim 1 wherein the copolymer has a hardness, shore Dscale, of about
 82. 6. The single layered balloon as in claim 1 whereinthe balloon has greater than 60% by weight polybutylene terephthalateand polytetramethylene ether glycol terephthalate copolymer.
 7. Thesingle layered balloon as in claim 1 wherein the balloon has greaterthan 95% by weight polybutylene terephthalate and polytetramethyleneether glycol terephthalate copolymer.
 8. The single layered balloon asin claim 1 wherein the copolymer has a flexural modulus of about 150,000psi to about 300,000 psi.
 9. The single layered balloon as in claim 1wherein the copolymer has a flexural modulus of about 175,000 psi. 10.The single layered balloon as in claim 1 wherein the balloon has acompliance of less than about 0.045 millimeters per atmosphere within aninflation pressure range of 135 psi to 270 psi.
 11. The single layeredballoon as in claim 1 wherein the balloon has a compliance of less thanabout 0.02 millimeters per atmosphere within an inflation 0.10 pressurerange of 135 psi to 270 psi.
 12. The balloon as in claim 1 wherein theballoon has a wall strength of at least about 10,000 psi to about 30,000psi.
 13. The balloon as in claim 1 wherein the balloon has a wallstrength of at least about 20,000 psi to about 30,000 psi.
 14. Theballoon as in claim 1 wherein the balloon has a wall strength of atleast about 25,000 psi to about 30,000 psi.
 15. The balloon as in claim1 wherein the balloon has a double wall thickness of no greater thanabout 0.0025 inches.
 16. The balloon as in claim 1 wherein the balloonhas a double wall thickness of no greater than about 0.0015 inches. 17.The balloon as in claim 1 wherein the balloon has a double wallthickness of no greater than about 0.0009 inches.
 18. The balloon as inclaim 1 wherein the balloon has an average rupture pressure of at leastabout 270 psi.
 19. The balloon as in claim 1 wherein the balloon has anaverage rupture pressure of at least about 345 psi.
 20. The balloon asin claim 1 wherein the balloon has an outer diameter of about 1.5millimeters to about 10 millimeters.
 21. The balloon as in claim 1wherein the balloon has an outer diameter of about 1.5 millimeters toabout 5 millimeters.
 22. An intraluminal balloon catheter, comprising:a) an elongated shaft having a proximal end, a distal end, an inflationlumen extending within at least a portion of a distal shaft section to alocation spaced proximally from the distal end; and b) a single layeredballoon for a medical device comprising a polymeric material, thepolymeric material being a substantially unblended copolymer ofpolybutylene terephthalate and polytetramethylene ether glycolterephthalate, the copolymer having a flexural modulus of greater thanabout 150,000 psi.
 23. The intraluminal catheter of claim 22 wherein theelongated shaft comprises an outer tubular member, and an inner tubularmember having a lumen and being disposed within the outer tubular memberand defining therewith the inflation lumen.
 24. The intraluminalcatheter of claim 22 further including a stent mounted on the balloon.25. A method for implanting a stent within a patient, comprising a)advancing within the patient's vasculature a catheter having a balloonon a distal shaft section, the balloon has a flexural modulus of about150,000 psi to about 300,000 psi and the balloon is formed from asubstantially unblended copolymer of polybutylene terephthalate andpolytetramethylene ether glycol terephthalate, the copolymer having aflexural modulus of greater than about 150,000 psi; b) positioning thecatheter so that at least a length of the balloon is across anon-dilated region within the patient's vasculature; and c) expandingthe balloon to simultaneously dilate the undilated lesion and implantthe stent.
 26. The method of claim 25 wherein the balloon has acompliance of less than about 0.045 mm/atm.
 27. The method of claim 25wherein the balloon has a compliance of less than about 0.02 mm/atm. 28.The method of claim 25 wherein the copolymer has a flexural modulus ofat least about 175,000 psi.